Alkylated diamines have been known for a substantial period of time and find use in the preparation of polyurethane elastomers. The diamines are typically used in that form as chain extenders for polyurethanes, i.e., forming a short chain urea linkage to strengthen the elastomer. As is known, the alkyl group alters the reactivity of the amine thus giving the composition unique processing properties for producing polyurethane elastomers.
A secondary use for the alkylated diamine products is in the manufacture of diisocyanates which are also suited for the synthesis of polyurethane elastomers. They can also be used for plasticizers, or as intermediates for the manufacture of pesticides and alkyd resin modifiers.
Two types of synthesis techniques have been used to produce alkylated aromatic amines, such as, an alkylated toluenediamine. One of the earliest techniques used to prepare an alkylated aromatic diamine employed a Friedel-Crafts alkylation of an aromatic hydrocarbon, then dinitration of the alkylated aromatic hydrocarbon followed by reduction of the nitro groups to amine groups. The diamine could be converted to the diisocyanate by reaction with phosgene. Another technique for producing alkylated aromatic amines involved nitration of the aromatic hydrocarbon, followed by reduction to the amine and alkylation of the amine. Representative patents illustrating various alkyl aromatic diamines and derivatives thereof are as follows:
U.S. Pat. No. 2,963,504 discloses a 2,6-diisocyanato-4-tert-butyltoluene composition which was formed from the 2,6-diamino-4-tert-butyltoluene derivative. No synthesis technique was shown. However, from the disclosed isomer structure, the product was produced by alkylating toluene, and then dinitrating the alkylated product followed by reducing the nitro group to amine.
In an article by Geuze, et al., preparation and proof of the constitution of 3,5-di-tert-butyltoluene, Rec. Trav. Pays-Bas, 75,306 (1956) and particularly examples 4 and 5 show the production of 2-amino-3,5-di-tert-butyltoluene and 2,6-diamino-3,5-di-tert-butyltoluene by the nitration and subsequent reduction of di-tertiarybutyltoluene.
U.S. Pat. No. 2,706,735 discloses 5-tert-butylisophthalonitrile. This derivative was prepared by reacting 5-tert-butylisophthalonitrile. This derivative was prepared by reacting 5-tert-butylisophthalic acid with ammonia over activated alumina at high temperature.
U.S. Pat. No. 3,991,023 discloses aromatic ester amine derivatives of benzoic acid and alkylated derivatives of aromatic ester amine derivatives of benzoic acid.
U.S. Pat. No. 4,365,051 discloses alkyl aromatic amine benzonitriles and alkyl aromatic amine benzoates as chain extenders for polyurethane manufacture;
U.S. Pat. No. 3,794,621 discloses aromatic amine esters as chain extenders for polyurethanes.
In all of the above aromatic amine compositions, the alkyl group is para to another organo group whether the organo group is a methyl group as in the case of toluene or an ester or nitrile group as in the case of aromatic esters or aromatic nitriles. As noted, these products are suited for use in the manufacture of isocyanates and polyurethanes.
Numerous aromatic amines having alkyl groups ortho to the amine, as opposed to being para to the amine, have also been used to produce polyurethane resins. In some instances, these amines have been either monoalkyl or dialkyl derivatives of the amines where the alkyl group has 2-3 carbon atoms. The art has recognized that these alkyl groups drastically alter the reactivity of the aromatic diamine. For example, ortho-alkylated diethyltoluenediamine is desirable for use in a urethane molding technique referred to as RIM (reaction injection molding).
U.S. Pat. Nos. 3,428,610 and 4,218,543 disclose the use of alkylated toluenediamines in the manufacture of polyurethane resins with the '543 patent showing its use in RIM manufacturing techniques. Alkylated diamines include 1-methyl-3,5-diethylphenylene-2,4-diamine and 1,3,5-trimethylphenylene-2,4-diamine. The diethyltoluenediamine derivative is referred to as diethyl TDA or DETDA and is probably the most widely used alkylated derivative of toluenediamine for RIM manufacture.
There is disclosure in many patents disclosing a variety of alkylated aromatic amines, but only a few of such amines have been synthesized. Some examples of alkylated aromatic amines are found in the following patents:
U.S. Pat. No. 2,762,845 shows 2,6-diethylaniline, isopropylaniline, ethyltoluidine and diethyl-m-toluidine.
British Pat. No. 846,226 discloses both ortho and para-tert-butyl aniline;
U.S. Pat. No. 3,275,690 discloses isopropyl- and diisopropylaniline, mono and di-tert-butylaniline; ethylaniline and dimethyldiethylaniline.
AS Pat. No. 1,051,271 (West German) shows mono, di, and triisopropylaniline; and U.S. Pat. No. 3,222,401 discloses cycloalkyl derivatives of aniline such as ortho-cyclooctylaniline, ortho and para-(dimethylcyclohexyl)aniline and ortho and para-methylcyclopentylaniline.
U.S. Pat. No. 4,440,952 shows the synthesis of 1-methyl-2,4-diamino-5-isopropylbenzene and 1-methyl-2,6-diamino-3-isopropylbenzene and the use of the 2,6-isomer as a chain extender for polyurethane formulation.
European Pat. No. 0069286 discloses various alkyl-substituted phenylenediamines as chain extenders for the production of polyurethanes by reaction injection molding techniques. Some of the compositions suggested as being suited for such use include the 1,3-dimethyl-5-tert-butyl-2,6-diaminobenzene. 2-methyl-4,6-di-tert-butyl-1,3-diaminobenzene 1,3-dimethyl-5-tert-amyl-2,4-diaminobenzene.
European Pat. No. 0107108 discloses the synthesis of C.sub.1-4 alkylated vicinal toluenediamines and their use as extender for the preparation of polyurethane-polymer elastomers. The example showed an ethylated vicinal toluenediamine.
U.S. Pat. No. 2,737,536 discloses the manufacture of a broad variety of tert-alkyl substituted aromatic hydrocarbons by reacting an aromatic hydrocarbon with a paraffinic hydrocarbon having a tertiary carbon atom in its structure in the presence of an olefinic hydrocarbon and an acidic alkylation catalyst. Mono and polyhydroxy benzenes, mono and polyaminobenzenes, hydroxyaromatic acids, aminophenols and many others were suggested as being alkylatable with paraffins such as methylbutane, methyl and dimethylpentanes and methylcyclopentanes and cycloalkanes. Catalysts suited for alkylation included acids such as hydrochloric acid.
Although a variety of alkylated aromatic diamine derivatives have been synthesized, e.g. diethyl TDA, such amines still present some problems to the formulator in terms of flexibility, handling and formulation. For example, in the manufacture of large molded parts even by RIM techniques, as in the manufacture of various automobile grilles, the reactivity of diethyl TDA may be too great to facilitate such molding techniques. They are also too reactive for the manufacture of cast elastomers. A second problem associated with alkylated aromatic diamines is that they are suspect carcinogens and present problems with respect to handling. This problem is similar to those aromatic amines having halogen atoms incorporated into the aromatic amine compositions to retard the activity of the amine in that such techniques have not altered the characteristics of the amine in terms of their mutagenic characteristics.